Unraveling the Morphological Evolution and Etching Kinetics of Porous Silicon Nanowires During Metal-Assisted Chemical Etching

Vinzons, Lester U.; Shu, Lei; Yip, SenPo; Wong, Chun Yuen; Chan, Leanne Lai Hang; Ho, Johnny C.

doi:10.1186/s11671-017-2156-z

Cited by 32 publications

(15 citation statements)

References 44 publications

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“…The morphological investigation of samples S1-S5 fabricated by the MACE technique revealed that both the length and the research papers diameter of the nanowires increase with increasing etching time. This is consistent with the results of other investigators (Huang et al, 2011;Razek et al, 2014;Vinzons et al, 2017;Bagal et al, 2018) [Figs. 1(a) and 1(b)].…”

Section: Resultssupporting

confidence: 94%

Unravelling the strain relaxation processes in silicon nanowire arrays by X-ray diffraction

et al. 2019

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Investigations performed on silicon nanowires of different lengths by scanning electron microscopy revealed coalescence processes in longer nanowires. Using X‐ray diffraction (XRD), it was found that the shape of the pole figure in reciprocal space is ellipsoidal. This is the signature of lattice defects generated by the relaxation of the strain concentrated in the coalescence regions. This observation is strengthened by the deviation of the XRD peaks from Gaussianity and the appearance of the acoustic phonon mode in the Raman spectrum. It implies that bending, torsion and structural defects coexist in the longer nanowires. To separate these effects, a grazing‐incidence XRD technique was conceived which allows the nanowire to be scanned along its entire length. Both ω and ϕ rocking curves were recorded, and their shapes were used to extract the bending and torsion profiles, respectively, along the nanowire length. Dips were found in both profiles of longer nanowires, while they are absent from shorter ones, and these dips correspond to the regions where both bending and torsion relax. The energy dissipated in the nanowires, which tracks the bending and torsion profiles, has been used to estimate the emergent dislocation density in nanowire arrays.

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Section: Resultssupporting

confidence: 94%

Unravelling the strain relaxation processes in silicon nanowire arrays by X-ray diffraction

et al. 2019

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“…Figure 4b gives an etching rate close to 0.152 µm/min. This linear relation has been investigated in literature but with different etching rate values [2,18,33]. The possible reasons behind this increase of SiNWs length with etching time was ascribed to the fact that etching was given more time to proceed and the solution had enough oxidizing species to oxidize and dissolve the formed SiO2.…”

Section: Etching Time Effect On Morphology Of Sinw Arraysmentioning

confidence: 87%

“…Our findings demonstrate that shorter SiNWs are much more optically and electrically active which is auspicious for the use in optoelectronic devices and solar cells applications.Nanomaterials 2020, 10, 404 2 of 18 time-consuming and therefore hindered their applications for commercialized products. In contrast, an effective and promising synthetic method namely metal assisted chemical etching (MACE) has been proposed [2,4,[18][19][20]. This technique is simple, rapid, low cost, and suitable for both industrial and laboratory scales.…”

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confidence: 99%

Elucidating the Effect of Etching Time Key-Parameter toward Optically and Electrically-Active Silicon Nanowires

et al. 2020

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In this work, vertically aligned silicon nanowires (SiNWs) with relatively high crystallinity have been fabricated through a facile, reliable, and cost-effective metal assisted chemical etching method. After introducing an itemized elucidation of the fabrication process, the effect of varying etching time on morphological, structural, optical, and electrical properties of SiNWs was analysed. The NWs length increased with increasing etching time, whereas the wires filling ratio decreased. The broadband photoluminescence (PL) emission was originated from self-generated silicon nanocrystallites (SiNCs) and their size were derived through an analytical model. FTIR spectroscopy confirms that the PL deterioration for extended time is owing to the restriction of excitation volume and therefore reduction of effective light-emitting crystallites. These SiNWs are very effective in reducing the reflectance to 9-15% in comparison with Si wafer. I-V characteristics revealed that the rectifying behaviour and the diode parameters calculated from conventional thermionic emission and Cheung's model depend on the geometry of SiNWs. We deduce that judicious control of etching time or otherwise SiNWs' length is the key to ensure better optical and electrical properties of SiNWs. Our findings demonstrate that shorter SiNWs are much more optically and electrically active which is auspicious for the use in optoelectronic devices and solar cells applications.Nanomaterials 2020, 10, 404 2 of 18 time-consuming and therefore hindered their applications for commercialized products. In contrast, an effective and promising synthetic method namely metal assisted chemical etching (MACE) has been proposed [2,4,[18][19][20]. This technique is simple, rapid, low cost, and suitable for both industrial and laboratory scales. Moreover, MACE allows to obtain high crystalline SiNWs quality, as well as an easy control of the different parameters including orientation, doping type, length, and diameter.The MACE method basically consists of two procedures, the formation of metal catalysts and the subsequent etching process which can be implemented either in a single step (1-MACE) [10,21] or in two steps (2-MACE) [17-20]. Moreover, the formation method, etching time, etching temperature, metal deposition time, and lastly the etchants' concentrations have a crucial influence on the morphology of SiNWs [2,5,17]. Ghosh et al. reported that SiNWs grown by MACE are usually covered with silicon nanocrystals due to the side wall etching and which are the origin of quantum confinement (QC) effects owing to their small dimensions [20]. Recently, several research groups have succeeded in the synthesis of optically-active SiNWs exhibiting a significant PL emission and a very low reflectance [3,4,17]. On the other hand, Qi et al. have demonstrated the fabrication of electrically-active SiNWs through heavily doped SiNWs with rough surface where a high Schottky barrier exists at the interface of SiNWs and the metal [22]. Nevertheless, further investigation is required t...

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“…This synthesis technique was made use of to test a Si nanowire solar cell which reported a low efficiency of 0.5% [328]. The most common type of wet etching-metal assisted chemical (MAC) etching involves a noble metal nanoparticle covering the Si wafer followed by reaction with an etchant [329][330][331]. The etchant facilitates oxidation of the Si wafer beneath the metal and as the process progresses, the Si beneath the metal nanoparticle is etched away forming Si nanowires [282].…”

Section: Fabrication Techniquesmentioning

confidence: 99%

Nanostructured photovoltaics

2019

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In this review, we begin by discussing the need for harnessing renewable energy resources in the context of global energy demands. A summary of firstand second-generation solar cells, their efficiency and grid parity is provided, followed by the need to reduce material and installation costs, and achieve higher efficiencies beyond the Shockley-Queisser limit imposed on single junction cells. We also discuss the specific advantages offered by nanomaterials in enhanced energy harvesting, what design platforms comprise nanostructured photovoltaics, and list the prominent categories of nanomaterials used in the design of third generation solar cells. We review the significant nanostructured photovoltaic platforms that have encouraging power conversion efficiencies, have the potential for long term stability (both structural and functional) and have received attention in the field. In addition to their operational principle, we highlight both their advantages and shortcomings, along with insights into possible improvements. We include alternate routes to improving power conversion efficiency, not by tuning material properties to match the solar spectrum but using additives and/or structural modifications to allow more efficient harvesting of sunlight, either by reducing losses or by altering the spectral properties. The properties of nanomaterials that make them well-suited as active materials in photovoltaic devices (broadband absorption, high quantum yield, etc.) also make them ideal candidates for luminescent solar concentrators (LSCs). These devices also harvest solar energy, but instead of directly allowing charge generation, they act as downconverters for other photovoltaic cells. We review dye, thin film, and quantum dot based LSCs that have garnered a lot of attention in recent years as these devices face a resurgence given the advances in materials science and engineering which have led to novel quantum dots and hybrid semiconductors. The review ends with where the future of nanostructured photovoltaics is headed, what device designs and materials development are needed to achieve efficiencies beyond the Shockley-Queisser limits and fulfil the goal of the 3rd and 4th generation photovoltaics.

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Unraveling the Morphological Evolution and Etching Kinetics of Porous Silicon Nanowires During Metal-Assisted Chemical Etching

Cited by 32 publications

References 44 publications

Unravelling the strain relaxation processes in silicon nanowire arrays by X-ray diffraction

Unravelling the strain relaxation processes in silicon nanowire arrays by X-ray diffraction

Elucidating the Effect of Etching Time Key-Parameter toward Optically and Electrically-Active Silicon Nanowires

Nanostructured photovoltaics

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